Stretch knitted fabrics are characterized by weaving, pretreatment, setting, dyeing and finishing processes: long routes, complex processes, many processes and most of them are carried out in sections. If the control is not good, it is easy to form fabric wrinkles in the production process; and Most of the folds are irreparable, directly causing the quality of the fabrics, leading to the price reduction of the fabrics, etc., causing unnecessary losses and impacts to the enterprise.
This article aims at some common wrinkles in the production process of knitted elastic fabrics, analyzes the causes and solutions, and hopes to provide useful help to the majority of knitting peers.
- The main causes of fabric wrinkles
(1) The basic structure of knitted fabrics is formed by numerous loops interlocked with each other. During the weaving process, it undergoes weaving tension fluctuations, tensile deformation, or artificial pulling during the production process, resulting in partial loop deformation.
(2) Wrinkles caused by equipment, technology and human factors in the process of loosening, pre-processing or pre-forming.
(3) The folding, squeezing, or heating and cooling rate of the fabric in the dye vat is too fast, and different fibers shrink differently in a short period of time, resulting in the displacement of the coil and the wrinkles caused by deformation.
(4) When the fabric is out of the setting machine, the surface of the fabric is not cooled enough, and the temperature of the fabric surface is too high, which causes the knitted fabric to be deformed by hot pressing in the cloth car.
(5) Because the elastic recovery rate of elastic yarn is higher than that of other fibers, it shrinks together with other fibers after being pulled, causing changes in the structure of the fabric during severe shrinkage, and then folding and squeezing the folds formed.
(6) For some special elastic yarns, the mutual adhesion effect between “elastic yarn-elastic yarn” and “elastic yarn-main fiber” will occur when encountering high temperatures above 120 °C. If the fabric surface is uneven at the moment of adhesion, Wrinkles, etc., the “curing effect” that occurs after adhesion, resulting in wrinkles on the knitted fabric surface.
- Fabric crease
(1) Weaving folds
Weaving folds refer to the folds formed during weaving, which mainly include edge folds, cloth head folds and side folds. This kind of wrinkle phenomenon should be discovered and adjusted in time during weaving, or should be paid attention to during the initial inspection of grey fabrics, and the weaving process should be discovered and adjusted in time, and solved in time.
(2) folds on the edge line
When the knitted fabric is weaved, if it is wound with a square support frame, two folds from the beginning to the end will be formed at the folded part. The reason for this is that the knitted fabric is folded in half and squeezed by the roller, one of which disappears after being cut by the slitter, and the other remains in the middle of the fabric, which is called the edge crimp.
The best way to solve the wrinkle of the edge holder is to use the automatic open-width coiling method. Now most of the new large circular machines have automatic open-width coiling devices; if there is no condition, the automatic open-width coiling method should be adopted. The weaving roll tension should be appropriately lowered within a reasonable range, and the roll pressure should be reduced as much as possible, and after the weaving and falling, the slitting machine should be used to open the rolls in time, so as to reduce the degree of folds in the blanking line as much as possible.
(3) Wrinkles at the head and tail of the cloth
Although the automatic open-width open-width coiling can overcome the problem of the edge line, improper operation can easily cause wrinkles at the head and tail of the cloth. The cloth head must be flat when it is rolled. It is best to have two people fully flatten the cloth head together before starting the machine, because once the cloth head is wrinkled or twisted and rolled, there will be obvious wrinkles in the cloth head ten yards after the cloth is loosened. If the embryonic cloth is piled up for a long time after the cloth is dropped, it will also cause the cloth surface to be indented or even crushed.
In order to reduce the wrinkle of the cloth head, some factories use double-sided adhesive cloth on the rolled up paper tube or rubber tube, and try to roll the cloth head as flat as possible. After the cloth tail is dropped, the cloth tails on both sides and the lower layer should be fully unfolded and knotted, which can avoid the formation of wrinkles when the cloth tail is slack.
In addition, it is best to use a rubber tube when the fabric is coiled, which can ensure the coiling quality, and can be reused, which meets the requirements of environmental protection. Due to the poor hardness of the paper tube, it is easy to deform or break after being pressed, resulting in new folds, indentations or pressure injuries on the cloth surface, and the damp paper tube will also cause the cloth to be stained.
(4) Folds on both sides
Products with high elastic fiber content, such as double-sided pure cotton, thick satin cloth, etc., will also form wrinkles on both sides of the embryo due to the resilience of the elastic fiber. Generally, these products do not need to be washed with water, and need to loosen the cloth first, and then pre-type. Care should be taken to minimize the parking time of the loose fabric in the cloth car, and pre-form in time to prevent the curling and stacking of the edges of the fabric from being too long and aggravating the wrinkling. Some weaving mills have formed wrinkles on both sides of the inward curling because the cloth head is not fully unfolded during the initial rolling of the embryonic cloth, which should be solved by timely feedback.
Three, loose cloth folds
For some embryo cloths that do not need to be washed with water (pre-treatment) and only need to be dyed directly after pre-type, it is required to arrange loose cloth first. Prepare for pre-styling or dyeing into the vat. If the equipment or process operation method of the loose cloth is not appropriate, it is easy to bring wrinkles on the cloth surface in the loose cloth stage.
(1) loose cloth equipment
The traditional cloth loosening equipment is to put the grey cloth into the cloth bucket first, and then it is pulled by the upper and lower rubber rollers running opposite to each other and sent to the swing frame, and then falls into the cloth loading car. The fabric is completely loosened by passive pulling, and the folds on the surface of the grey fabric are clearly visible; the new type of loosening equipment is equipped with a speed-adjusting motor, which adopts active unwinding instead of passive pulling; in addition, the loosening frame is also installed. The cloth guide roller is controlled by the speed regulating motor, and the fabric is completely loosened in a loose state, which solves the wrinkle of the cloth surface caused by the equipment.
(2) loose cloth operation
In addition to the equipment problem, the key is how to standardize the operation, that is, the coordination between the running speed of the loose cloth speed regulating motor and the speed of the cloth guide roller of the loose cloth frame. The operator is required to pay attention to observe the condition of the cloth surface after loosening the cloth, and try to maintain the loose state as much as possible to avoid the phenomenon of tension and stretching of the cloth surface. The level of workshop management is the core of this problem.
- Pre-treatment of folds
Most stretch knitted fabrics are pre-treated (washed) before they are pre-shaped, and most of them use open-width pre-treatment.
On the one hand, it can eliminate the residual stress formed in the weaving process of the embryo fabric, remove the oil stains and dirt during the weaving and warping, and prevent the oil stains from being fixed on the fabric during pre-forming, and the color spots and color difference after dyeing will affect the quality of the finished product. On the other hand, it can also improve the feel, luster, permeability, softness and so on of the fabric. Open-width water washing equipment is used for pre-treatment, in which the way of feeding the cloth, the running state of the spreading roller, the temperature of the cloth surface after treatment and the size of the stacking cloth are the main factors that cause wrinkles in the pre-treatment.
(1) Feeding method
Processed stretch knitted fabrics cannot be stretched by machine or artificial tension. In the actual production process, it often occurs that the cloth loosening device of the washing machine is out of sync with the cloth guide roller, and the cloth surface is wrinkled after being pulled and squeezed. The new equipment solves this problem well after adding the speed control device.
(2) The running state of the spreading roller
If the spreading roller (spreading roller) of the open-width washing (pre-treatment) machine is affected by failure or belt slippage, the spreading or spreading effect is affected, and obvious creases can be seen during washing and falling.
(3) The temperature of the cloth surface after treatment
The scouring temperature of the two open-width washing tanks is above 98°C, and then it enters into a warm wash at about 80°C for one time, pickling and neutralization for one time, and finally cold washing. It is necessary to strictly abide by the process discipline, and do not arbitrarily increase the speed of the car to prevent the creases caused by the liquid on the cloth surface and the high temperature and hot pressing.
(4) Stacked cloth after washing
The preformed cloth after washing should be pre-formed as soon as possible, and do not pile up too much, too high, or too long in the cloth car. The reasons are as follows: avoid the flow color caused by dirty washing; at this time, the plasticity of the cloth surface is still large, and some cloth The sides are also curled, which will create new folds in the cloth as the pressure increases.
- Pre-defined crease
Presetting is a key process in the production of elastic knitted fabrics. Its main purpose is to eliminate and improve the internal stress of elastic yarns, the tensile deformation caused by weaving, to stabilize the structure of the loops, and to make the fabric surface smooth and wrinkle-free. It can also reduce and prevent dyeing. New folds are formed during the process. The main factors for the formation of wrinkles in the fabric during the pre-forming process are: the operating state of the equipment, the pre-forming temperature and time (vehicle speed), and the control of the fabric width.
(1) The operating state of the equipment
In fact, the wrinkling phenomenon on the surface of the fabric is caused by improper equipment or human operation during the processing. Pre-configured equipment failures can also cause fabric creases. For example, the opening position of the distribution gear before feeding the cloth should be appropriately enlarged. If the opening is too small, the grey cloth will be squeezed, and the cloth surface will easily form wrinkles;
Check whether the spreading roller before the cloth enters the roller is running normally, if the belt slips for a long time, the cloth cannot be fully unfolded, and creases will also occur after being rolled by the roller due to folding.
In the hollow position of the overfeeding section of the tenter setting machine, the traditional equipment is to fix two stainless steel frames to hold the fabric, and the fabric is dragged on the surface into the oven. Affects the effect of the cloth surface.
The new type of sizing equipment is improved to drive the conveyor belt by the motor, and change the passive to the active mode of active conveying, which solves this problem well.
(2) Pre-type temperature and time (vehicle speed)
As mentioned above, the purpose of pre-forming is mainly to eliminate wrinkles during weaving and pretreatment, improve the uniformity of the molecular structure of the (elastic) non-crystalline region of the fiber, improve the dimensional stability of the fabric, and prevent the dyeing cylinder from damp heat. , Shallow edges caused by folds or curling on the cloth surface.
Production practice shows that the pre-forming effect determines the flatness and stability of the finished fabric, and the pre-forming temperature and action time (vehicle speed) are the main factors affecting the wrinkle and dimensional stability of the fabric. As long as the pre-forming process is well controlled and the foundation is laid, the final product can have good results.
The pre-type (action) time is inversely proportional to the temperature, while the vehicle speed is proportional to the temperature. The higher the temperature, the faster the vehicle speed; otherwise, it is slower. The pre-forming temperature and time (vehicle speed) should be selected according to the type and characteristics of the elastic yarn and main fiber.
For knitted fabrics containing spandex, due to the limitation of spandex on the setting temperature, the pre-setting temperature can only be set between 190 and 205 °C, and the “feeling” of the main fiber cannot be taken care of (even if the main fiber is damaged, the main fiber can only be “Endure”), the preset speed is controlled at about 20 ~ 30m/min; and the preset temperature of knitted elastic fabrics using some polyolefin elastic yarns, according to the characteristics of the main fiber, between 120 ~ 210 ℃ Arbitrary selection, the best pre-forming temperature, vehicle speed (setting time), etc. for different fiber types.
(3) Control of the flatness of the cloth surface
The control of the flatness of the pre-formed fabric is the square meter weight (quality) and width of the pre-formed fabric, which is actually the control of the fabric overfeed.
For different stretch yarns, the width, grammage and overfeed amount of the pre-fabricated fabrics are different. For elastic knitted fabrics containing spandex elastic yarn, the predetermined width is 5-10 cm wider than that of the finished product, and the gram weight is slightly larger than 5-10 g/m2. It cannot be removed after dyeing and finishing.
It is advisable to properly control the overfeed amount of the pre-shaped (dry-shaped) door width. The amount of overfeeding should not be too much. Once the overfeeding amount is too much, shrinkage wrinkles will be formed on the cloth surface, which cannot be removed even after dyeing and finishing.
- The folds in the dyeing tank
The main factors that cause the wrinkle of elastic knitted fabrics in the dyeing cylinder are: nozzle pressure, running speed of the roller, winding, cylinder pressing, cloth blocking and dyeing heating and cooling rate.
(1) Nozzle pressure and roller speed
The coordination and coordination between the pressure of the nozzle of the dyeing machine and the speed of the rotating roller during the dyeing process is controlled and mastered by the dyeing operator according to the process practice and for different types of cloth. For heavy fabric dyeing machines, the nozzle pressure should be appropriately increased, and the speed of the lifting roller should be slowed down, so as to smoothly push the fabric to run normally; on the contrary, for light and thin fabrics, the nozzle pressure should be appropriately reduced and the speed of the lifting roller should be increased. Reduces the tension between the water flow and the lift rollers and the fabric, thereby reducing the wrinkling caused by the stretching of the fabric surface in the dye vat.
(2) Wrapping the car, pressing the cylinder, and blocking the cloth
The wrinkle of the cloth surface caused by the wrapping, pressing and blocking of the cloth in the dyeing tank is generally caused by the following reasons:
First, the dyeing amount is too large, the liquor ratio is small, the fabric has a long cycle in the tank, and the fabric is folded and squeezed with each other, and the cloth surface is easy to form folds like chicken feet. The dyeing tank must pay attention to the size of the tank. Generally, the production is arranged according to 60% to 70% of the volume of the tank, so as to avoid the wrinkling phenomenon caused by the poor running of the fabric in the tank.
The second is the broken cloth caused by the defects of the blank cloth or the weak joints, which are blocked in the cylinder, and the blocked cloth folds formed by the water flushing for a long time under high temperature conditions.
The third is the regenerated cellulose fibers with poor wet strength, such as modal, viscose fiber, bamboo fiber fabrics, or very thin fabrics, when adding color in the dyeing vat, and the color repairing time is too long, causing the cloth to break and the cylinder to wrinkle; this Cut samples of similar products to match the colors. If the color difference is found to be large, you should wash out the tank first, and then enter the tank for dyeing if the color is close to the color; if the color pattern is serious, negotiate with the customer to change it to a dark color. The fiber is broken in the cylinder due to poor wet strength.
(3) Dyeing heating and cooling rate
The heating and cooling rate of the dyeing process not only affects the levelness of the fabric, but also affects the feel and wrinkle degree of the dyed fabric.
If the thermal processing temperature is not properly controlled, the surface temperature of the fabric will be heated or cooled, and the fabric will be wrinkled due to the thermal shrinkage of the fibers. In production practice, there have been folds on the cloth surface, sometimes even serious folds, after the operator violated the process regulations and changed the heating and cooling from computer automatic control to manual, especially when the cooling rate was too fast. Therefore, the dyeing process is strictly in accordance with the computer program, and the slow heating and cooling is not only conducive to level dyeing, but also helps to reduce the wrinkles on the cloth surface.
Seven, finished product stereotyped folds
After pre-setting the elastic knitted fabric, the finished product is strictly a drying process. The purpose is to eliminate a small amount of wrinkles on the cloth surface caused by heat shrinkage in the dyeing cylinder, and re-end the fabric surface with smoothness and flatness to achieve the required width and gram weight; but also pay attention to the final product setting temperature, the running state of the setting machine, especially The cooling effect of the cloth surface after the finished product is finalized, and the stacking of the finished product in the cloth car, if the control is improper, new wrinkles will also appear on the cloth surface.
(1) Finished product setting temperature
The elastic knitted fabric adopts a relatively high setting temperature in the pre-forming stage, which plays a good role in preventing wrinkles that may be formed during the subsequent dyeing and wet heat processing. Therefore, the selection of the final product setting temperature can be 5-10°C lower than that of the predetermined type, and the cotton or regenerated cellulose fibers can be lower, about 10-30°C lower. According to experience, the surface effect of the finished product after setting is improved as the setting temperature increases, and the wrinkles are reduced. A few cases with a small amount of wrinkles after the dyeing vat can be improved by appropriately increasing the setting temperature of the finished product, but it cannot be completely solved.
(2) The running state of the setting machine
When the finished product is finalized, attention should be paid to observe the running state of the machine to prevent the weft deviation or even wrinkles caused by the deviation of the fabric, the needle falling off or the abnormal spreader.
(3) Cooling of the finished cloth surface
After the fabric is heat-set, the fabric surface should be cooled at an appropriate rate in the rear section of the setting machine. If the cooling is not enough, the speed of the vehicle is too fast or the cooling effect is not achieved, it may cause new wrinkles in the fabric.
At present, there are two main cooling methods for the tenter setting machine: one is to blow cold air; the other is to enter the cold air roller after passing through the cold air area, and the fabric is cooled by contacting the surface of the cold air roller. From the practical application point of view, if the temperature of the cloth surface at the time of dropping the cloth drops below 50 °C, it will obviously improve the wrinkling phenomenon of the cloth surface.
(4) Stacking of finished products
The stacking method of the finished products after finalization is also very important. The finished fabrics should always be kept in an open width state when they fall in the cloth car, so as to avoid the phenomenon of random throwing, throwing and random placement, and avoid artificially caused